Generally, Brushless DC Motor (BLDC Motor) has a simple structure and a high efficiency, and is widely used in industry. Typically, an armature formed by applying a current to the coil is used as a BLDC motor stator and is a permanent magnet formed by repeated N and S poles and is used as a rotor.
In order that the BLDC motor is rotated continuously, it is necessary to form a continuous rotating magnetic field of the BLDC motor, and since the stator flux is rotated in synchronization with the magnetic field of the permanent magnets of the rotor, the position information of the rotor may be required. In other words, in order to form a continuous rotating magnetic field, it is necessary that commutation of the current flowing to each phase of coils of the armature be performed at the appropriate time, and it is required that the position of the rotor be precisely recognized for proper commutation. Herein, commutation represents changing the current direction of the motor stator coil to allow the rotor to be rotated.
For smooth operation of the BLDC motor, it is necessary that the position of the rotor and the phase current commutation time be exactly matched, and for this, a device configured to detect the position of the rotor is required. Generally, for the detection of the position of the rotor, a position detection sensor such as a Hall sensor, a resolver element and an encoder may be used. However, since manufacturing costs have increased and a driving circuit has become complicated recently, a sensorless method which can drive a motor without a sensor for the detection of the position of the rotor is used.
The method for driving a sensorless BLDC motor includes extracting a back electromotive force (EMF) generated in stator coil of each phase while the motor is rotated, and estimating position information of the rotor and each phase current commutation time by using a zero cross point of the phase back EMF.